What a kid's question? That is impossible for sure. There are so many reasons why. I can tell you one of them - there are a lot of bitcoin holders and they just don't want to sell bitcoins not to government, not to anyone else.
A lot of people wants to hold their bitcoins and expecially tol sell it to government.
Well, he's just saying "If" despite the chance of bitcoin getting owned by the big banks which really low but there's still a chance, he's just asking how if all the big banks own bitcoin.
if from my opinion, bitcoin will remain decentralized, its system nature which is blockchain is designed to be decentralized at the start, none of us can rule and can't force to take people's money, just the big banks owning big portion of bitcoin and could possibly manipulate the market.